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.Dd April 2, 2022
.Dt ALARM 3
.Os
.Sh NAME
.Nm alarm
.Nd set signal timer alarm
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft unsigned int
.Fn alarm "unsigned int seconds"
.Sh DESCRIPTION
.Bf -symbolic
This interface is made obsolete by
.Xr setitimer 2 .
.Ef
.Pp
The
.Fn alarm
function sets a timer to deliver the signal
.Dv SIGALRM
to the calling process after the specified number of
.Fa seconds .
If an alarm has already been set with
.Fn alarm
but has not been delivered, another call to
.Fn alarm
will supersede the prior call.
The request
.Fn alarm "0"
voids the current
alarm and the signal SIGALRM will not be delivered.
.Pp
Due to
.Xr setitimer 2
restriction the maximum number of
.Fa seconds
allowed is 100,000,000.
.Sh RETURN VALUES
The return value of
.Fn alarm
is the amount of time left on the timer from a previous call to
.Fn alarm .
If no alarm is currently set, the return value is 0.
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigsuspend 2 ,
.Xr signal 3 ,
.Xr sleep 3 ,
.Xr ualarm 3 ,
.Xr usleep 3
.\" .Sh STANDARDS
.\" The
.\" .Fn alarm
.\" function conforms to
.\" .St -p1003.1-90 .
.Sh HISTORY
An
.Fn alarm
system call appeared in the Programmer's Workbench (PWB/UNIX)
and was ported to
.At v7 .
For
.Bx 4.1c ,
it was reimplemented as a wrapper around the
.Xr setitimer 2
system call.
